The invention relates to a method of producing a film or a layer with a surface structure at least on one side of a base film and, on the other side, in register with said surface structure, a structural or two-dimensional pattern, which are produced by means of a first roller and a second roller, provided with a circumferential structure, the rollers being driven in approximately equally fast, but opposite rotation, and the film or the layer being produced by applying a layer of thermoplastic polymer to a film fed to the second roller via the first roller and by irradiating through the base film the polymer layer bearing against the circumference of the second roller in order to cure it, and also relates to a suitable apparatus for said method.
The applicant""s EP-B 655 032 discloses how an anti-copy film is produced from transparent material and line- or strip-shaped screens in defined offset arrangement onto both surfaces of the film by printing and/or photographic technology by applying a photosensitive coating, in particular a photoresist coating, to one side of the film, exposing it to (UV) light through a mask and developing it and subsequently applying a further photosensitive coating to the other side of the film, exposing it to (U) light through a mask and developing it. A particularly good register of the line or strip screens is achieved in this case if the second photosensitive coating is exposed through the first, already developed coating.
U.S. Pat. No. 3,241,429 also discloses 3-dimensional panorama pictures which are provided with paper as the base film or directly comprise a layer of plastic lenses, an emulsion being printed either onto the paper or onto the rear side of the layer of lenses. To obtain register of the lenses with the print on the rear side, incisions or punched openings in the film are used, with the aid of which the printing operation takes place in register.
U.S. Pat. No. 4,420,502 disclose an apparatus for producing a film with a predetermined, finely defined surface structure on one side, a first, smooth-surfaced cylindrical roller and a second cylindrical roller with a structured circumference being driven and a flowable, uncured thermocurable resin material and a transparent film being introduced in to the nip between them, and a film or a layer with a defined structure being obtained on the film by subsequent UV curing. The UV curing takes place through the film directly on the second roller.
A single-layer structured film is obtained, which can be used in particular for the purpose of 3-D pictures and is also known from U.S. Pat. No. 4,414,316, a description of which follows. In it, a flexible, composite film with a lenticular surface comprises in a known way a base film and a transparent thermocurable layer, which has lenticular forms, the focusing plane of the lenticular forms lying substantially at the rear side of the base film. The thermocurable layer comprises a thermocurable polymer, which is cured by means of UV light. The known film is intended for producing 3-dimensional representations or photographs, in that the film is laminated onto stereographic printed images.
A film structured on one side is also known from WO 94/01288. In it, cylindrical lenses are provided on one side and screening strips may be produced on the rear side by printing, but without specifying how a fixed relative arrangement of the lenses with respect to the position of the screening strips is technically achieved. A film for anti-copying purposes cannot be produced on the basis of this document.
It is therefore an object of the present invention to specify methods and apparatuses which make it possible to produce economically films or layers structured in-register on two sides.
The features of the method by which this object is achieved by the present invention were described at the outset.
It is surprisingly possible here, after curing the surface structure layer on one side of the base film to provide the other side of the base film with a further layer, likewise having a structural or 2-dimensional pattern, and to cure the latter through the surface structure layer on one side by radiation curing, to be precise while the surface structure layer on one side is still in engagement with the circumferential structure of the second roller, with the result that an absolutely in-register formation of the layer on the rear side of the base film is achieved, meeting the given tolerance of the film or layer produced.
The method further comprises using a film or a layer which has as a surface structure on one side a multiplicity of identical, parallel, elongate lenticular structures, in particular of cylindrically arched form, and is provided on the other side with mutually assigned parallel lines or grooves or ridges (or xe2x80x9cbarsxe2x80x9d) in register with said structures.
The film or the layer may also be formed with a multiplicity of parallel arcuate lenses as the surface structure.
The surface structure on the other side may also be formed by a multiplicity of parallel ridges, in particular of rectangular form.
It is expedient if the lenticular structure on one side and the parallel lines, grooves or ridges on the other side are produced after each other in time, in particular immediately after each other, and in register with each other.
The lenses and ridges may advantageously consist of a UV-curable polymer, in particular an acrylic resin. It is also possible, for reducing transparency, to add to the polymer, in particular the acrylic resin, pigment as a filler accounting for up to about 30% by weight.
It is likewise advantageous to provide the ridges with optically opacifying layers, in particular to print said layers on.
The number of such opacifying layers is at least two, preferably eight.
In any event, for applications of the film or layer produced for anti-copying purposesxe2x80x94the maximum transparency of the ridges should be about 7%. This ensures that the viewing-angle-dependent properties of the anti-copy film can be realized.
In order that the legibility of the document is ensured, the width of the ridges is chosen such that they cover, and consequently render opaque from an approximately perpendicular viewing direction, at most about 80% of the surface area of the film or of the layer.
In a preferred apparatus according to the invention there is a third roller, which is arranged downstream of the first two rollers, is driven equally fast and in the opposite direction to the second roller and is provided with a structural or 2-dimensional pattern on the circumference, a further layer being applied by means of a further application device to the other side of the base film, which has been coated and cured on one side, and is subsequently cured (on the other side) by means of a radiation source.
The second roller expediently has as the circumferential structure a multiplicity of identical parallel, elongate cylindrically lenticular grooves, in particular of cylindrically arched form. The grooves may also have an arcuate form in cross-section.
The third roller is expediently formed with a circumferential structure comprising a multiplicity of parallel grooves, in particular of rectangular form.
The grooves are produced very exactly and reproducibly.
The first roller is expediently produced with a smooth circumferential surface.
In practice, at the first roller there is provided a contact roller, by means of which the base film for the production of a film or a layer is fed to the circumference of the first roller.
The first roller may advantageously serve as a master drive roller for controlling the rotational speed of the first and third rollers,
It is favorable in practice if the second roller is designed to be axially adjustable by means of an adjusting device, in particular on an eccentric basis, with respect to the first and third rollers. Similarly, the third roller may be designed to be axially adjustable with respect to the first and second rollers.
The adjusting device may, in a simple way, substantially comprise a thrust element which is connected to the axially adjustable roller and to which an eccentric shaft is fastened.
It is also favorable if the not respectively axially adjustable rollers are mounted by means of a swivelling away or drawing away de vice, for simple and fast threading in of the base film.
A swivelling mechanism, formed by an eccentric mounting, may be favorably used for this.
A coater with a coating gap may be used as the application device for the layer material, and a lifting-off device for the coater may likewise be provided for threading in the base film.
Furthermore, it is advantageous in practice if bearing means are used, in which two of the first to third rollers can be set with respect to the other (remaining) roller in their parellelism to the other (remaining) roller.
For driving each of the three rollers, a disc-armature motor with interposed gear transmission and a sychronism control may advantageously be provided.
It is very favorable if the application device is a curtain coater which has a housing with light shielding devices, the latter including elements made of PTFE.
Furthermore it is very favorable if the application device consists of fine feed regulation elements. These elements are piston housings with needles moving transverse the coating are of the roller.
In practice, a nip setting device may be provided for the first nip between the first and second rollers and a further nip setting device may be provided for the second nip between the second and third rollers.
An unwinding station for the base film is equipped with a compensating roller control and is arranged upstream of the production device for the film or the layer, in order to obtain a constant tape tension which can be set.
A further drive station with compensating roller control may be advantageously provided downstream of the production device in the running direction of the film or the layer, in order to be able to set another suitable tape tension.
Furthermore, if the ridges are to be provided with opacifying layers for reducing transparency, it is expedient to arrange a printing station, for printing onto the ridges on the rear side of the base film, downstream of the further drive station in the running direction of the film or the layer.
If desired, a station for applying an adhesive to the film or the layer may expediently also be provided downstream of the printing station.